4g22

Publication Abstract from PubMed

Chlorogenic acids (CGA) are a group of phenolic secondary metabolites produced by certain plant species and an important component of coffee. The CGAs have been implicated in biotic and abiotic stress responses, while the related shikimate esters are key intermediates for lignin biosynthesis. Here, two hydroxycinnamoyl-CoA shikimate/ quinate hydroxycinnamoyl-transferases (HCT/HQT) from Coffea canephora were biochemically characterized. We show for the first time that, in vitro, HCT is capable of synthesizing the 3,5-O-dicaffeoylquinic acid diester (diCQA), a major constituent of the immature coffee grain. In order to further understand the substrate specificity and catalytic mechanism of the HCT/HQT, we performed structural and mutagnesis studies of HCT. The three-dimensional structure of a native HCT and a proteolytically stable lysine mutant enabled the identification of important residues involved in substrate specificity and catalysis. Site-directed mutagenesis confirmed the role of residues Leu-400 and Phe-402 in substrate specificity and His-153 and the Val-31 to Pro-37 loop in catalysis. In addition, the His-154-Asn mutant was observed to produce 4-fold more diCGAs compared to the native protein. These data provide the first structural characterization of a HCT and, in conjunction with the biochemical and mutagenesis studies presented here, delineate the underlying molecular level determinants for substrate specificity and catalysis. This work has potential applications in fine-tuning the levels of shikimate and quinate esters (CGAs including diCGAs), in different plant species in order to generate reduced or elevated levels of the desired target compounds.

A STRUCTURAL BASIS FOR THE BIOSYNTHESIS OF THE MAJOR CHLOROGENIC ACIDS FOUND IN COFFEE.,Lallemand LA, Zubieta C, Lee SG, Wang Y, Acajjaoui S, Timmins J, McSweeney S, Jez JM, McCarthy JG, McCarthy AA Plant Physiol. 2012 Jul 20. PMID:22822210^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.